The invention relates to processes used in integrated circuit fabrication for removing photoresist and organic and inorganic residues or polymers from the surface of semiconductor devices, and more particularly to processes for removing photoresist and polymers or residues from the surface of integrated circuit devices with a combination of gasses, including water vapor.
Conventional fabrication of an integrated circuit device typically involves placing numerous device structures, such as MOFSETs, bipolar transistors, and doped contact regions, on a single monolithic substrate. The device structures are then electrically interconnected with horizontal conductive lines or structures formed in layers and vertical conductive structures called vias between layers, with dielectric material disposed between the conductive structures so as to implement desired circuit function.
During the fabrication of semiconductor devices, it is typical to perform a series of steps resulting in the etching of via holes, trenches, and other structures into one or more layers. After this step, it is necessary to remove the photoresist in a process typically referred to as ashing. Furthermore, a residue, often called a sidewall polymer or a veil, is typically formed on the walls of the features during these process steps, and the residues can include both organic and inorganic components. It is well known in the art that the presence of such residues and polymers affects the reliability of the semiconductor devices. One of the major challenges facing current manufacturing processes is the requirement for complete removal of such residues.
There are many known methods for ashing the resist and removing such residues. Currently preferred methods frequently use fluorine containing gasses such as CF4, NF3, and SF6, usually in the presence of O2, to facilitate the removal of the residues. However, the fluorine based etchants also attack the metal alloy layers and the dielectric oxide layers present on the semiconductor device. It is known in the art that the addition of water vapor to the etchant gasses, particularly to etchant gasses comprising CF4 and O2, significantly improves the selectivity of the process, causing the etch rate of oxides and metal layers to drop significantly. A number of etching or stripping methods have been developed using water vapor.
Commercially available water vapor delivery systems for use in semiconductor fabrication currently utilizes liquid water for the water vapor source. Generally, the liquid water is heated in a vessel, and vapors are drawn off through a heated mass flow controller and a heated series of valves and lines to the reaction chamber. However, the use of liquid water as a water vapor source has presented a number of difficulties. For example, if the vessel is not at an adequate temperature, there may not be enough vapor for the reaction, and an adequate heat-up time, often several hours, must be allowed. Water, especially very pure deionized water, has excellent solvating properties, and thus tends to acquire organic and inorganic contaminants from a variety of sources including the pipes, fittings, and adhesives in the water delivery lines of the equipment in which the water is used. Also, especially in stagnant regions, water may contain microorganisms, which can be a continual source of contaminants. Typically, the flow of water vapor is controlled by the use of special, heated mass flow controllers that operate by sensing the pressure before and after the regulating valve, and then adjust the flow by opening or closing the valve based on the pressure difference. These mass flow controllers are sensitive to their absolute inlet and outlet pressures, and will not operate correctly if they are not within a narrow pressure tolerance. This makes water vapor difficult to control, especially when used with other non-condensable gasses that may backstream into the mass flow controller. Furthermore, the water vapor may cool and form microscopic droplets, which can contaminate a wafer""s surface. Lastly, liquid water source water vapor systems require a vapor bypass assembly to keep the vapor flowing continuously, even when the water vapor is not being used in the reaction cahmber.
What is needed is a method for removing photoresist and other polymers or residues that avoids the disadvantages of the prior art.
The invention is a novel processes used in integrated circuit fabrication for removing photoresist and or post-etch polymers or residues from the surface of integrated circuit devices with a combination of gasses, including water vapor created using a catalytic moisture generator.
To address the problems commonly experienced with current semiconductor fabrication processes using water vapor derived from liquid water based water, a novel method has been developed. In the method of the invention, water vapor is formed by the reaction of hydrogen and oxygen in a catalytic moisture generator. The hydrogen is carried in a mixture commonly called forming gas, in which the hydrogen is heavily diluted with an inert gas, such as helium or nitrogen, so that it is less flammable. Oxygen is added to the forming gas in the presence of the catalyst to form the water vapor. The use of this type of water vapor source is novel to process equipment used in the semiconductor industry.
In one embodiment, the method of the invention is a method for removing photoresist and organic and inorganic residues from the surface of semiconductor devices comprising the steps of: (a) placing a semiconductor device, having a residue formed thereon, into a reaction chamber, (b) introducing etchant gasses into the reaction chamber, wherein the etchant gasses preferably include at least one fluorine containing gas, and water vapor generated by introducing O2 and an H2 containing forming gas into a catalytic moisture generator to create the water vapor, (c) applying energy to the etchant gasses to generate a plasma, and (d) exposing the semiconductor device in the reaction chamber to the plasma for a selected period of time. In this method, the fluorine containing gas may comprise one or more of CF4, NF3, and SF6. It is preferable that, the hydrogen containing forming gas includes a helium or argon dilutant. The hydrogen preferably makes up 1% to 25% of the forming gas, and more preferably 4% to 6% of the forming gas. Generally, the O2 and H2 are combined in stoichiometric amounts, however, in alternate methods the relative quantities of each can be varied. In some embodiments of the method, the etchant gas further includes N2. The water vapor can be introduced together with, or separately from, the other etchant gasses.
A second embodiment of the method of the invention is a method for controlling the amount of water vapor introduced to a reaction chamber during a semiconductor device fabrication process comprising the steps of: (a) providing a reaction chamber having a catalytic moisture generator in gas communication therewith, (b) placing a semiconductor device into the reaction chamber, (c) introducing etchant gasses into the reaction chamber, wherein the etchant gasses include water vapor generated by introducing O2, and a forming gas including H2 and at least one dilutant gas, into a catalytic moisture generator, and (c) controlling the flow rate of water vapor into the reaction chamber by controlling the flow rate of the H2 containing forming gas and the flow rate of the O2 gas into the catalytic moisture generator. In some embodiments of this method, the H2 comprises between 1% and 20% of the volume of the hydrogen containing forming gas, but more preferably the H2 comprises between 4% and 6% of the hydrogen containing forming gas. In other embodiments, the hydrogen containing forming gas further includes one or more of helium, argon, or nitrogen. Preferably the H2 and the O2 are introduced into the catalytic moisture generator in stoichiometric quantities, so that an output of the catalytic moisture generator includes insignificant quantities of any gasses other than water vapor and a dilutant gas. However, in some embodiments of the method it may be preferable to introduce excess hydrogen into the catalytic moisture generator so that the resulting output of the catalytic moisture generator includes hydrogen, water vapor, and a dilutant gas. In still other embodiments, it may be preferable to introduce excess oxygen into the catalytic moisture generator so that the resulting output of the catalytic moisture generator includes oxygen, water vapor, and a dilutant gas.